thread error when creating massive number of threads

I was doing some testing with Python threads and found that when I try
to create 300 threads one immediately after another, the 255th thread
can't be created. The error message I get is:

thread.error: can't start new thread

When I put a pause between the creation of each thread of .1 second, I
have the same problem. If I pause .2 seconds between creation of
threads, no more problem.

Why is this? If it helps, I'm using python 2.3.3 on Debian SID.

Thanks.

Randall